Fusing apparatus

ABSTRACT

A fuser unit useful in copier machines, such as zerographic-type machines, is shown, in which the support base on which toner particles form an image and the toner particles are heated to effect fusion of the particles and bonding of the fused toner to the support base. A conventional zerographic machine is shown which mounts therein the fuser unit comprising a low voltage source in the form of a high turns ratio transformer, a temperature controller, foil-heating elements suspended in frames and a temperature sensor having first thermal response located on one of the foil elements. An alternating current source in the machine is used as the input to the system via the temperature controller. The foil heater, which has no thermal or electrical insulation, and hence minimal thermal lag, has minimal mass with substantial radiant heat generating surface area thereby permitting a very fast warmup time-within a copy cycle-so as to be maintained in a deenergized standby condition between copy cycles. The low voltage source obviates shock hazards in the machine. The support base can be moved at a constant rate of speed or intermittently if desired. Another embodiment employs a rotating drum adapted to carry a support base, which has been subjected to a liquid development treatment, through a fuser unit. The drum may be heated if desired. A foil heater is mounted between two current distributing support electrodes, one electrode being fixed; the other, biased to tension the foil against the drum in intimate heat transfer relationship to the support base passing therebetween. As in the first embodiment a temperature controller, alternating current source and a temperature sensor having low mass are employed. The secondary is comprised of a large cross-sectional area bus bar whose ends are electrically joined to the foil through the current distributing electrodes and whose control section passes through the iron core of the transformer thereby providing a single turn secondary winding. The cross section of the bus bar is selected to minimize voltage drop and associated power loss with the substantial current flows necessary. This type of transformer secondary can also be used in the first embodiment.

United States Patent [72] Inventor Charles D. Flanagan Attleboro, Mass.

[21] Appl. No. 694,914

[22] Filed Jan. 2, 1968 [45] Patented I Aug. 17, 1971 [73] Assignee Texas Instrument Incorporated Dallas, Tex.

[54] FUSING APPARATUS 9 Claims, 3 Drawing Figs.

52 use: 219/216,

219/388 51 1nt.Cl 1105b1/00 s01 FieldofSearch 219/344,

[56] 7 References Cited UNlTED STATES PATENTS 3,082,313 3/1963 Jepson et a1. 219/441 2,285,776 6/1942 Maccoy 219/44 FPD X 2,600,485 6/1952 Cox 338/212 X 2,600,486 6/1952 Cox 338/212 X 2,961,522 11/1960 Hammer... 219/345 X 3,076,083 1/1963 Codichini. 219/216 X 3,099,540 7/1963 Eisler 219/549 X 3,275,802 9/1966 Vandivere et al... 219/345 X 3,397,301 8/1968 Hager, Jr 219/345 1,920,685 8/1933 Evans.. 219/311 3,316,387 4/1967 Waldron 219/553 FOREIGN PATENTS 866,096 4/1961 Great Britain 219/354 975,038 10/1950 France 219/345 673,925 11/1963 Canada 219/355 547,670 4/1932 Germany..... 338/316 738,848 10/1955 Great Britain 219/553 Primary Examiner-J. V. Truhe Assistant Examiner-C. L. Albritton Attorneysl-larold Levine, Edward .1. Connors, Jr., John A.

Haug and James P. McAndrews ABSTRACT: A fuser unit useful in copier machines, such as zerographic-type machines, is shown, in which the support base on which toner particles form an image and the toner particles are heated to effect fusion of the particles and bonding of the fused toner to the support base. A conventional zerographic machine is shown which mounts therein the fuser unit comprising a low voltage source in the form of a high turns ratio transformer, a temperature controller, foil-heating elements suspended in frames and a temperature sensor having first thermal response located on one of the foil elements. An alternating current source in the machine is used as the input to the system via the temperature controller. The foil heater, which has no thermal or electrical insulation, and hence minimal thermal lag, has minimal mass with substantial radiant heat generating surface area thereby permitting a very fast warmup time-within a copy cycle-so as to be maintained in a deenergized standby condition between copy cycles. The low voltage source obviates shock hazards in the machine. The support base can be moved at a constant rate of speed or intermittently if desired.

Another embodiment employs a rotating drum adapted to carry a support base, which has been subjected to a liquid development treatment, through a fuser unit. The drum may be heated if desired. A foil heater is mounted between two current distributing support electrodes, one electrode being fixed; the other, biased to tension the foil against the drum in intimate heat transfer relationship to the support base passing therebetween. As in the first embodiment a temperature controller, alternating current source and a temperature sensor having low mass are employed. The secondary is comprised of a large cross-sectional area bus bar whose ends are electrically joined to the foil through the current distributing electrodes and whose control section passes through the iron core of the transformer thereby providing a single tum secondary winding. The cross section of the bus bar is selected to minimize voltage drop and associated power loss with the substantial current flows, necessary, This type of transformer secondary can also be used in the first embodiment.

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PATEHTEIJ mun 71971 SHEET 1 BF 2 Inventor; Charles D. Plan by A4 fj/lttjy.

PATEHTEIII nus 1 7 I97! SHEET 2 or 2 Charles D. 1 Ian 3 a FUSING APPARATUS BACKGROUND OF THE INVENTION This invention relates to improvements in reproduction systems and, particularly, to improvements in image fusing devices utilized in certain of these systems. A

For convenience of illustration, the first embodiment of the invention is described with reference to its use as a heat fuser for a zerographic powder image. However, it is to be understood that it may be employed with equal facility in other fields, especially in other methods for reproducing images.

In the process of zerography, a zerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the light intensities that reach them, thereby creating an electrostatic latent image in the photoconductive layer. Development of the latent image is effected with an electrostatically charged, finely divided material, such as an electroscopic powder, which is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a zerographic powder image pattern corresponding to the electrostatic latent image. Thereafter, the developed zerographic powder image is usually transferred to a support surface to which it may be fixed by any suitable means.

In zerography it is normal to develop images with a powder or toner formed of any of a variety of pigmented thermoplastic resins that have been developed for the purpose. These resinous powders are compounded for producing dense images of high resolution and to have characteristics permitting convenience in handling. Such developing materials are compounded to permit them to be fixed or bonded to the surface of a transfer material either by heat fusing or vapor fusing techniques in accordance with the particular application in which they are employed. The individual particles or resins soften and coalesce when heated or plasticized by solvent so that they become sticky and readily adhere to the surface of the transfer material.

In order to fuse resinous powder images, it is necessary to heat the powder and the paper to which it is to be fused, to a relatively high temperature. The temperature must be kept fairly constant; if the temperature fluctuates too low or the time that the support material is exposed to the temperature is too short, the resinous powder will not properly adhere to the support surface; and if the temperature is too high or the time of exposure is too long, there is a tendency for the support material to discolor or scorch.

Many types of fusers have been tried but found lacking in various respects. Existing commercial fusing equipment usually consists of either an oven where the support material is placed on a plate and is inserted into the oven and manually withdrawn after a predetermined length of time or automatically as in automatic zerographic reproducing machines wherein the support material is carried on a belt or conveyor mechanism past or through a fuser unit at a predetermined rate. The present invention comprises a unit wherein the support material is carried past one or more foil heating elements which have a very short warmup time, low electrical voltage requirements, which do not need thermal or electrical insulation which would tend to lengthen warmup time and which are completely safe to the user as well as to the support medium passing therethrough.

An object of the invention is the provision of improved fusing apparatus for fixing zerographic powder images to support surfaces. Another object is the provision of a heating device useful with a liquid toner for affixing to a support surface. Another object of the invention is the provision of improved apparatus for affixing toner particles to support surfaces. Still another object of the invention is the provision of apparatus for fusing of resinous powder images deposited on sheets of paper, or the like, and retained thereon by electrostatic latent charges. It is a further object of the invention to provide novel heat fusing apparatus for fusing images having higher thermal efficiencies than fusing apparatus heretofore. Another object of the invention is the provision of a fuser unit which can be maintained in standby condition between copy cycles, has a response time within the copy cycle and yet presents no shock hazards to a user thereof.

The novel features of the invention, as wellas additional objects and advantages thereof, will be understood more fully from the following description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic representation of a zerographic unit embodying the fusing apparatus of the invention;

FIG. 2 is an isometric view of the fusing apparatus in accordance with one embodiment of the invention; and

FIG. 3 is a partial elevational and schematic representation of a second embodiment of the invention.

Dimensions of certain of the parts as shown in the drawings may have been modified for the purpose of clarity of illustration.

It is desirable in most copying systems when in a standby condition that no electrical power is supplied during these periods between copy operations. This requires extremely rapid warmup of the fuser unit with concomitant-high input power levels when the copy cycle is initiated in order to prevent using more time than that required for the copy cycle time. It has been found that the minimum practical warmup time is determined by the maximum acceptablepeak power level and is in the order of 2-3 seconds. However, a convenient measure to use as a guide for optimizing heater warmup is thatwhich is referred to herein as the time required for the copy cycle, i.e., the time between the initiation of the copy cycle and the time when the copy or support base is presented to the fuser unit. This is normally in the vicinity of 5 seconds. The heater of the instant invention is designed to come up to full heat within the length of time resulting in optimum fuser operation.

The instant invention uses a heater, the structure of which has virtually no mass, no electrical insulation and hence a minimal thermal lag or inertia. This also obviates the possibility of damaging an insulating layer used in" conventional systems due to the response time of a temperature sensor which would be caused by the time lag incident to thermal conduction through such a layer. By the time a temperature sensor sees an increase in temperature to a critical level and accordingly causes a decrease in power input to safer levels, the insulating layer contiguous to the heater element is normally at a somewhat higher temperature causing either deterioration of the insulating material or an inefficient system. In the instant invention, all of the heating element structure is active in the generation radiation and convection of heat to the system. Another advantage provided by the invention is that a low voltage source is provided thereby minimizing shock hazards.

For a general understanding of the zerographic processing system in which the invention is incorporated, reference may be had to FIG. 1, in which the various system components are schematically illustrated. The original to be reproduced, in any form, is placed so that the image is projected through lens 12 onto the surface of zerographic plate, drum 14. Zerographic drum 14 includes a suitable mounting in the frame of the machine for rotation and is driven counterclockwise by motor 16 at a constant rate of speed. The drum surface comprises a layer of photoconductive-insulating material on a conductive backing that is sensitized prior to exposure by means of a corona generating device 18, energized from a suitable high potential source. Exposure to the light discharges the photoconductive layer in the areas struck by light whereby there remains on the drum latent electrostatic image in configuration corresponding to the light image projected from the original. As the drum surface continues its movement, the

electrostatic latent passes through a developing station 20in whicha'two component developing material 22, of a standard type, is. cascaded over the drum surface by .means of a developing apparatus 29. f In the developing apparatus, developing material is carried upwardly by conveyor 26 driven by suitable drive means from motor 28 and is released onto shoot 30 from which it cascades down over the drum surface. Toner component 32 of developing material 22 which is consumed in developing is stored in dispenser 34 and is released in controlled amounts by gate 36.

.After developing, the zerographic powder image passes a discharge station at which the drum surface is illuminated by a lamp 38 whereby residual charges on the nonimage areas of the drum surfaces are completely discharged. Thereafter, the powder image passes through an image transfer station 40 at which the powder image is electrostatically-transferred to a support surface by means of a second corona generating dev'ice42, also energized froma suitable potential source.

The-support surface 45 to which the powder image is transferred may be of any convenient type, such aspaper, that is obtained from a supply roll 44 is fed over' guide falls 46, 48, and caused to come into surface contact with drum 14 in the immediate vicinity of transfer corona generating device42. After transfer, support surface 45 is separated from the drum surface and guided through the fusing apparatus of the invention designated 60 to be described in detail infra. Thereafter, the support surface is fed over. guide roll 50 and suitable tensioning rolls not shown onto a takeup roll 52 driven by motor 54. The drum surface then passes through a cleaning station in which its surface is brushed by a brush 56, rotated by motor 57, whereby residual developing material remaining on the drum is removed. Thereafter, the drum surface passes through a second discharge station where it is illuminated by a fluorescent lamp 58 so that thedrum surface in this region is completely flooded with light to remove an electrostatic charge that may remain thereon. Suitable light shields are provided in the system to prevent any light rays from reaching the drumfsurface, other than the projected image, during the period of drum travel immediately prior to sensitization by the corona generating device 18 until after the drum surface completely passesthrough the developing station 20.

\ Erna-ruse. unit 60 of the invention will now be described in detail by referring 'more particularly toFlG. 2. As will beQunderstood,' the apparatuswill be adapted for fusing images onto continuous web in.the manner of FIG. 1 or alternatively can be employed for fusing individual cut sheets for which the mechanism of the fuser includes transportmeans including intermittentmotion means to move the sheet past the heat source.-

The heat fuser as shown, comprises an upper and lowerheating assembly 62, 64 respectively. It should be noted that it may be preferable in some circumstances to employ only one assembly. Upper assembly 62 includes a generally rectangular frame within which is mounted a very thin foil heater element 68"v of stainless steel or other suitable heater material suspended between current distributing supports 70, 72. Current distributing support 72 is fixedly mounted on one end of frame 66 while current distributing support v70 is flexibly mounted by springs 74 which tension the foil element and suspend foil 68 apart from the frame 66. Foil element 68'is connected to the secondary of a high turns ratio transformer by lead 78. The lower assembly includes'a foil-heating element 80 connected to the other side of the secondary by lead 82. Although not shown the foil 80 is suspended within frame 84 in a manner similar to foil element 68 in frame 66. An aperture 86 is provided in frame 84 (as well as a similar aperture in frame 66) to permit radiant heat transfer from the foils to a support base passing therebetween. Foil element 80 is electrically connected to foil element 68 by lead 88, terminal 90, pigtail 92 and current distributing support 70. The foils are electrically isolated from the frame members by any convenient means, such as by using anodized aluminum for the frame members. Alternatively, the frame could be constructed of insulating material such as a high heat resistant resinous material. A thin guide rod 94 is attached to upperand lower frame members 66, 84 to preclude contact of the support base passing between the heating assemblies with the foil elements. A temperature sensor having very low mass is located under foil patch 96 welded to foil 68 as at 98. The temperature sensor must have low thermal mass to enable a fast response time to make it compatible with the warmup characteristics of the foil. It will be noted that the patch is welded generally on,a line perpendicular to current flow avoiding the possibility of forming a shunt' path for the current I with a concomitant disturbance to uniform heat generation. A closure member 100 is placed over upper assembly 62 and attached thereto. A similar closure member is provided for assembly 64 but is not shown.

The primary winding of transformer 76 is connected to a temperature controller 102 by leads 104, 106. An alternating current source 108 which may be obtained within the machine is connected to controllerl02 by leads 1'10, 112. The tem-- perature sensor is connected to controller l02by leads 114, 116. The temperature controller may be an on/off type but preferably is a proportional controller as disclosed in U.S. ap-

plication Ser. No. 454,776, filed May 11, 1965 assigned to the assignee of the instant invention. The temperatureof the foil is sensed by the temperature sensor which is in intimate heatconductive relation therewith. The temperature sensor sends an electrical signal to the controller 102 to vary the energization of the primary transformer winding. This controller thereupon energizes the primary winding oftransformer 76 'to a degree necessary to cause the required current to flow through the secondaryandhence the heating foil element 68, 80 to keep them at a preselected temperature level.

The secondary winding is chosen so that a low voltage is seen across it, e.g., approximately 12 volts, so that even if a user should contact the heater no harm would result. Due to the minimal mass of the foil which is in the range of 0.0005 to 0.003 inches in thickness the time required to bring the heat up to full temperature isalmost instantaneous whichpermits the heater to be deenergized between uses of the machine. No warmup time or preenergization period is required. Due to the low mass and large area providing radiant heat energy the temperature which the heating elements rnust be'elevated to is less that that of a standard heater used in various' prior art fusers such as coils, radiant heat panels and thelike. It has been found that a temperature in the vicinity of 600 F. is sufficient for the foilelements to raise the temperature ofa support base to the desired level of approximately 325 F during the typical transit time thereby to effect optimum fusing of the toner and bonding to the paper support base. This is accomplished within the copy cycle so that no additional warmup time is required.

When the copy cycle is initiated an inrush of current passes through heating foil elements 68, raising the temperature thereof to full level by the time the copy has gone through the developing process and is presented to unit 60 for fusing.

Another embodiment is shown in FIG. 3 which is particularly adaptable for use-with liquid developing materials. In the apparatus a rotatable support drum which may or may not be heated, provided with a layer of feltlike material 122, acts as the support surface for the support base to be heated which moves in the direction of arrow 124 between felt 122 and foilheating element 126 extending between currentdistributing fixed support 129, and movable support 131. A tension spring 133 biases current distributing support 131 so that foil 126 is in intimate but flexiblecontact with felt 122. Supports 129,

131 also act as the electrical terminals of foil 126 and are elecwith the necessary substantial current flow. The primary of transformer 128, a standard winding about core 132 is electrically connected to temperature controller 102 by leads 134, 136. An alternating current source 138, which may be obtained from any convenient source in the reproducing machine is electrically connected to controller 102 by leads 140, 142. Temperature sensor 144 is maintained in intimate heat transfer relation to foil 126 by foil patch 146 attached to foil element 126 and is connected to controller 102 by leads 148, 150.

It 'will be noted that the heating element in both embodiments of the invention have substantial area, the one in FIG. 3 extends across the width of drum 120 yet has virtually no mass due to the thinness of the foil. The thin foil and large surface area results in relatively low thermal density in terms of watts per square inch of heater surface while still maintaining the low thermal mass compared to conventional heaters. In both embodiments a low voltage source is supplied to minimize shock hazards while permitting an almost instantaneous response.

It is within the purview of this invention to employ in the FIG. 1 embodiment the transformer secondary shown and described in FIG. 3.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

lt is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

1 claim:

1. Apparatus for fusing zerographic-type powder images on a support base moving through a copier machine comprising:

a. a copier machine having means for moving a support base along a path of movement,

b. an elongated foil-heating element supported only at two opposite ends biased into a plane generally parallel to the path of movement,

c. a frame in which the foil element is mounted,

d. biasing means suspending the foil within the frame,

e. a support guide member mounted on the frame intermediate the frame and path of movement,

f. means to sense the temperature of the foil, and

g. means to vary the energization of heater current in accordance with the sensed temperature of the foil.

2. Apparatus according to claim 1 in which the means to vary the heater energization includes a temperature controller.

3. Apparatus for fusing zerographic-type powder images on a support base moving through a copier machine comprising:

a. a copier machine having means for moving a support base along a path of movement,

b. an elongated foil-heating element having a longitudinal axis supported only at two opposite ends having heat transfer surface area located in a plane generally parallel to the path of movement,

c. a frame in which the foil element is mounted,

d. biasing means suspending the foil within the frame, and

e. means including a stepdown transformer to energize the heater.

4. Apparatus according to claim 3 in which the transformer includes a single turn secondary.

5. Apparatus according to claim 3 including:

g. a temperature sensor placed on the foil element and a foil patch welded to the foil on a line generally perpendicular to the longitudinal axis and forming a pocket in which the temperature sensor is retained.

6. Apparatus according to claim 5 in which the temperature sensor is electrically connected to a temperature controller and the primary of the transformer is electrically connected to the temperature controller, the secondary of the transformer is connected to the foil element and a source of alternating current is supplied to the temperature controller.

7. Apparatus according to claim 3 in which a second elongated foil element supported only at two opposite ends is placed generally parallel to the first and on the other side of the path of the support base.

8. Apparatus according to claim 3 in which a cylindrical drum is provided to transport the support base and the foil element is biased against a portion of the periphery of the drum.

9. Apparatus for fusing zerographic-type powder images on a support surface moving through a copier machine comprising a copier machine having means for moving the support surface along a path of movement,

two generally rectangular frames mounted in the machine and arranged parallel to the path of movement of the support surface, one frame above the path, the other frame below the path,

a guide member mounted on each frame intermediate the frame and the path of movement,

a foil suspended in each frame, supported only at two opposite ends, and kept under tension by spring means, the foil offering a large radiant surface area relative to its mass and having no electrical insulation, and

a stepdown transformer connected to the foil so that upon the initiation of the copy cycle of the machine the power input causes the foil to come up to operating temperature with minimal time lag. 

1. Apparatus for fusing zerographic-type powder images on a support base moving through a copier machine comprising: a. a copier machine having means for moving a support base along a path of movement, b. an elongated foil-heating element supported only at two opposite ends biased into a plane generally parallel to the path of movement, c. a frame in which the foil element is mounted, d. biasing means suspending the foil within the frame, e. a support guide member mounted on the frame intermediate the frame and path of movement, f. means to sense the temperature of the foil, and g. means to vary the energization of heater current in accordance with the sensed temperature of the foil.
 2. Apparatus according to claim 1 in which the means to vary the heater energization includes a temperature controller.
 3. Apparatus for fusing zerographic-type powder images on a support base moving through a copier machine comprising: a. a copier machine having means for moving a support base along a path of movement, b. an elongated foil-heating element having a longitudinal axis supported only at two opposite ends having heat transfer surface area located in a plane generally parallel to the path of movement, c. a frame in which the foil element is mounted, d. biasing means suspending the foil within the frame, and e. means including a stepdown transformer to energize the heater.
 4. Apparatus according to claim 3 in which the transfoRmer includes a single turn secondary.
 5. Apparatus according to claim 3 including: g. a temperature sensor placed on the foil element, and h. a foil patch welded to the foil on a line generally perpendicular to the longitudinal axis and forming a pocket in which the temperature sensor is retained.
 6. Apparatus according to claim 5 in which the temperature sensor is electrically connected to a temperature controller and the primary of the transformer is electrically connected to the temperature controller, the secondary of the transformer is connected to the foil element and a source of alternating current is supplied to the temperature controller.
 7. Apparatus according to claim 3 in which a second elongated foil element supported only at two opposite ends is placed generally parallel to the first and on the other side of the path of the support base.
 8. Apparatus according to claim 3 in which a cylindrical drum is provided to transport the support base and the foil element is biased against a portion of the periphery of the drum.
 9. Apparatus for fusing zerographic-type powder images on a support surface moving through a copier machine comprising a copier machine having means for moving the support surface along a path of movement, two generally rectangular frames mounted in the machine and arranged parallel to the path of movement of the support surface, one frame above the path, the other frame below the path, a guide member mounted on each frame intermediate the frame and the path of movement, a foil suspended in each frame, supported only at two opposite ends, and kept under tension by spring means, the foil offering a large radiant surface area relative to its mass and having no electrical insulation, and a stepdown transformer connected to the foil so that upon the initiation of the copy cycle of the machine the power input causes the foil to come up to operating temperature with minimal time lag. 